Most people who pay for a website every month own exactly one part of it. Usually not the part they think.
This sounds like a trick question and it is not. It has a specific answer, and the answer changes what happens to your business if a company changes its pricing, its terms, or its mind.
Your domain name — yourbusiness.com — assuming it is registered in your name and you can log in to the account it lives in. This is the valuable one. It is the address on your business cards, in your Google listing, and in every email you have ever sent. It is genuinely yours, it moves with you, and it costs about $20 a year.
Your content — your words, your photos, your logo. Yours in the copyright sense. Whether you can easily get them out is a separate question, and the answer is usually "partly".
The site itself. The layout, the templates, the way it all fits together — that is the platform's, built with the platform's tools, and it does not leave. There is no export button that hands you a working website. Squarespace will give you a partial dump of your text and images; it will not give you your site.
The hosting. Obviously. Stop paying and it stops serving.
Increasingly, the terms. Prices go up. Features move between tiers. Something that was included becomes an add-on. None of that is unusual or dishonest — it is just what it means to build on land you do not own.
That is not a scare story. Platforms rarely disappear. But the question is a good way to see the actual shape of the arrangement, which is easy to lose track of when everything is working and the bill is small.
That last point matters more than it sounds. The goal is not to move you from renting someone else's platform to depending on me instead. It is for you to end up holding everything, including the ability to fire me.
Every account involved in your website should be registered to your email address, with a password you hold — the domain registrar, the hosting, the form handling, all of it. People who build websites can be added as a helper on your accounts and removed again. It should never be the other way around.
If you are talking to anyone about a website and they want the accounts in their name "to keep it simple", that is the moment to slow down. Simple for whom.